Catheters are often used for diagnostic or therapeutic procedures that require the insertion of a catheter into the circulatory system to reach a predetermined site such as an artery near the heart. The catheter is positioned at the desired site by alternately advancing a guidewire ahead of the catheter from a body access site, through the circulatory system until reaching the desired site. The path that the guidewire and catheter must follow is tortuous.
The catheter and guidewire must be quite flexible in order to follow the tortuous path to the desired site. However, because these guidewires are advanced through the circulatory system by applying a torque to the proximal end of the guidewire which is located at an external site, the guidewire must have sufficient column strength to allow the distal end of the guidewire to be manipulated from the external access site, which can be more than 150 centimeters from the distal end.
Current catheter guidewire designs attempt to meet these requirements by incorporating a tapered distal end region to increase the flexibility of the guidewire's distal end. Unfortunately, this reduces the column strength of the distal end. To remedy this problem, a wire coil is brazed or soldered onto the tapered section of the wire to increase the column strength of the tapered wire section without losing the flexibility. Guidewires of this type are disclosed in U.S. Pat. Nos. 4,538,622, 4,545,390, 4,582,181 and 4,846,186.
Unfortunately, this type of guidewire construction requires many manufacturing steps including the tapering of the guidewire, the forming of the wire coil, cutting the coil to the desired length and fastening the coil to the distal end section of the guidewire. This method of construction is not only time consuming and costly to manufacture, but it also presents the danger of having the coil separate from the wire while it is in the patient.
One attempt to eliminate the drawbacks of the current designs was to enclose the tapered distal end section in a polymer sleeve as described in U.S. Pat. No. 5,095,915. The addition of the polymeric sleeve is used to increase column strength of the tapered distal end of the catheter guidewire without using a coil. Axially spaced grooves are then cut into the polymeric sleeve to increase the bending flexibility of the sleeve. Unfortunately, this method also requires the use of multiple manufacturing steps and parts to form the guidewire. In addition, there is the potential danger of having the polymeric sleeve separating from the wire within a vessel of the patient. Moreover, because the distal end of the wire is tapered, the strength of the distal end is reduced.
Therefore, there arises a need for a catheter guidewire that is made from a single piece having a flexible distal tip to allow the guidewire to follow the tortuous path and having a sufficient column strength to allow manipulation of the catheter guidewire from an external access site.